I don't think you need to worry about the tsunami. Mito is far enough away from the coast to be virtually unaffected by the tsunami. The earthquake would have hit Mito fairly hard, but in all of Ibaraki prefecture there were only 24 deaths from the earthquake. It was something like magnitude 6 in Ibaraki.
Its possible the apartment they lived in was damaged bad enough so that they have to move. Their surname is unusual enough so that they should pop up in a search if they are active on social media, but I looked and couldn't find anything except some old references. My guess is they are still in Mito. Hopefully something will pop up.
Putting the family name here in kanji for reference, which I think should be OK since its not pointing to anything too private.
佐谷